Internal jet interactions in a fluidic oscillator at low flow rate

Abstract

This study focuses on the internal jet interactions and the oscillation mechanism of the feedback-free fluidic oscillator at low flow rate, corresponding to a Reynolds number of 1,350 (based on exit nozzle width and average exit velocity). Particle image velocimetry (PIV) was used in this study with a refractive index-matched fluid to minimize reflections that would otherwise occur at the fluid-acrylic interface in the test setup. A simple microphone-tube sensor configuration generated a reference signal, with a phase-averaging method based on each quarter period for velocity time history reconstruction. PIV results revealed the existence of a vortex of fluctuating size, shape, and strength on each side of the oscillator; and two transient vortices that are formed in the dome region of the oscillator by each of the jets once per period. The dome vortices periodically bifurcate each of the jets and transfer some of the kinetic energy of that jet to the opposing jet. This kinetic energy transfer mechanism dictates the dominance of either jet at the exit, and this mechanism repeats itself to sustain the oscillations created by the fluidic oscillator. At this flow rate, the two jets form a continuous mutual collision, and the jets are never completely cut off from the exit. The oscillatory behavior at this flow rate is due to a complex combination of jet interactions and bifurcations, vortex-shear layer interactions, vortex-wall interactions, and saddle point formations.